FIG. 1 of the drawings shows a typical image capturing system comprising a lens system 100 and a sensor (or film) 102 to capture an image illuminated by a light source 104.
In image capturing systems involving the lenses such as the one shown in FIG. 1 of the drawings, the light distribution by the lens system is non-uniform, causing a captured image to have some light intensity fall-off toward the edges of the image. This artifact is called the lens shading artifact or vignette.
FIG. 2 of the drawings illustrates the effect of the lens shading artifact on a captured image. Referring to FIG. 2, it will be seen that a captured image 200 includes a central circular region 202 where the light intensity is the brightest. The light intensity falls off radially away from the center region 202. Edges 204 at the corners at the image 200 show the greatest fell off in light intensity.
The lens shading artifact may be removed by multiplying the light intensity I(x, y) at the image location (x, y) by a lens shading correction amount L(x, y)Icorrected(x,y)=I(x,y)×L(x,y)
In reality, for image capturing systems that include an image sensor, the sensor might contribute offset terms that would make the Equation (1) more complex. The offset terms are not considered so as not to obscure the invention. However, one skilled in the art will know how to modify Equation (1) with the offset terms.
The lens shading artifact may be modeled and the function L(x, y) may be computed from the model. Because the function L(x, y) is a two-dimensional (2D) function with two variables x and y, its model tends to be complicated and expensive to implement in hardware.